Noise reducing method for radio portable terminal

ABSTRACT

A noise reducing method for a radio portable terminal having a radio section for transmitting and receiving radio data, a CPU (Central Processing Unit), connected to the radio section and incorporating a cache, for performing predetermined data processing, and an external memory connected to the CPU, reads an internal operation program runnable only in the CPU from the external memory and stores the internal operation program in the cache prior to reception of the radio data, and then executes only the internal operation program. In this manner, this method suppresses access to the external memory, thereby reducing noise.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application is a division of application Ser. No.09/426,942, filed Oct. 26, 1999, now pending, and based on JapanesePatent Application No. 10-305837, filed Oct. 27, 1998, by KenichiYoshida. This application claims only subject matter disclosed in theparent application and therefore presents no new matter.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a noise reducing method for aradio portable terminal, and, more particularly, to a noise reducingmethod for reducing noise generated by a central processing unit (CPU)in a radio portable terminal.

[0004] 2. Description of the Related Art

[0005] Conventional measures against noise in a radio portable terminalinclude a scheme of stopping the operation of the CPU in the radioportable terminal at the time of receiving data and a scheme ofshielding the CPU, an external memory and so forth. Recently, there hasbeen a demand for an improvement on the processing performance of radioportable terminals, which has led to an increasing use of fast CPUs. Itis not therefore a good idea to stop the operation of the CPU.

[0006] When the CPU in a radio portable terminal accesses an externalmemory, large noise is generated. To suppress noise by reducing thenumber of accesses to the external memory, the conventional radioportable terminals use an exclusive read only memory (ROM) or randomaccess memory (RAM) incorporated in the CPU.

[0007] For example, Japanese Patent No. 2748773 (hereinafter called“first prior art”)

[0008] discloses a method of reducing noise generated by the operationof a CPU used in a radio receiving circuit, thereby improving thesensitivity of the radio receiving circuit.

[0009]FIG. 7 presents a structural diagram of a conventional radioportable terminal which is disclosed in the first prior art. The radioportable terminal shown in FIG. 7 comprises a microprocessor 300 whichoperates in a dual mode, an interface 205, a user interface 117, a modeswitch 308, a RAM 202 and a ROM 201.

[0010] This dual-mode microprocessor 300 has a RAM 301 and ROM 302 asits internal memories. The ROM 302 may be a masked ROM or an erasableprogrammable ROM (EPROM). This dual-mode microprocessor 300 may furtherinclude an electrically erasable programmable ROM (EEPROM) 303 which canbe used for permanent storage of a program or data.

[0011] The mode switch 308 is connected to first-mode and second-modeselect terminals (not shown) via a plurality of conductors 309. The userinterface 117 is connected via a control input conductor 307 to themicroprocessor 300 to provide the microprocessor 300 with predeterminedinformation. Specifically, the control input conductor 307 providesmeans for starting the mode change (between the first mode and thesecond mode) in the dual-mode microprocessor 300. The user interface 117is connected to the microprocessor 300 by a plurality of data inputlines 305 and a plurality of data output lines 306.

[0012] It is understood from experiments that the level of noisegenerated in the dual-mode microprocessor 300 can be reducedconsiderably when the microprocessor 300 operates only in internal mode(the aforementioned first mode) where the individual internal memories301, 302 and 303 are mainly used, as compared with a case where themicroprocessor 300 operates in external mode (the second mode) in whichan external memory is used. In the first prior art, therefore, thedual-mode microprocessor 300 operates while being switched to asingle-chip mode, i.e., the internal mode, or an extension mode, i.e.,the external mode. Specifically, the basic operation is carried out insingle-chip mode in which case noise to be generated by an operation toaccess an external device connected to the CPU or an external memory viaan external bus is minimized. When the microprocessor 300 is operatingin this single-chip mode, the ROM 201 and RAM 202 as external memoriesare inactive. Further, no signals are flowing through an externaladdress bus 203 and a data bus 204. The level of noise to be generatedis reduced by setting those external memories and external busesinactive and optimizing the time for which the microprocessor 300operates in single-chip mode.

[0013] To reduce the level of noise generated by the microprocessor 300while the radio portable terminal is receiving radio data, the programsthat are stored in the dual-mode microprocessor 300 should becategorized. More specifically, individual modules (routines) includedin the programs are associated with the respective functions of theradio portable terminal by systematically analyzing the codes of eachprogram. Based on those functions, the modules can be separated into twomain categories.

[0014] The modules of the first category are associated with thefunctions that are susceptible to the influence of noise, e.g., theradio receiving function. The modules of the first category are executedinside the microprocessor 300 when it is operating in single-chip mode.

[0015] The modules of the second category are associated with thefunctions that are insusceptible to the influence of noise, such as theradio transmitting function, the function for changing the operationmode of the radio portable terminal and the function to communicatedwith a user. The modules of the second category operate in extensionmode using the ROM 201 and RAM 202 as external memories, the externaladdress bus 203 and the data bus 204.

[0016] It is ideal to store all the modules of the first category in theinternal ROM (EPROM) 302, more desirably, into the internal EEPROM 303of the microprocessor 300. The EEPROM 303 may further retain data whichvaries only occasionally. To effectively use an additional memory whichis provided by the internal RAM 301, the modules of the first categoryare further separated into a main algorithm and sub algorithms.

[0017] The main algorithm of the first category consists of an activeprogram which runs continuously. The sub algorithms are programs whichare called as needed and frequently use the external address bus, andeach sub algorithm is formed by, for example, a delay loop or a loopwhich monitors a change in the status of the input or the like. Thesoftware is designed in such a way that the main algorithm of the firstcategory is permanently saved in the internal ROM 302 (EPROM) of themicroprocessor 300 and the sub algorithms of the first category arestored first in the external memories 201 and 202. Each sub algorithm istransferred to the internal RAM 301 every time it is called or only whenits specific module is needed. Once the module of any sub algorithm isloaded into the internal RAM 301, this sub algorithm is executed whenthe microprocessor 300 returns to the single-chip mode or the internalmode.

[0018] Unexamined Japanese Patent Publication (KOKAI) No. Hei 7-203510(hereinafter called “second prior art”) discloses a method of reducingthe frequency of the system reference clock when a radio portableterminal is used.

[0019] Another Unexamined Japanese Patent Publication (KOKAI) No. Hei8-70258 (hereinafter called “third prior art”) discloses a method ofchanging the frequency of the reference clock in such a manner as toavoid interference between the frequency that is used in thetransmission and reception operations of a radio portable terminal andthe harmonics of the reference clock.

[0020] The aforementioned first prior art has the following problems.

[0021] The first problem is the necessity of an exclusive CPU. That is,because a RAM and ROM should be incorporated in a CPU in the first priorart, a conventional ordinary CPU cannot achieve the object.

[0022] The second problem lies in that the RAM should be of an exclusivetype for the following reason. As a cache in a general-purpose CPU iscapable of automatically caching a saved command or data, such a commandor data in the incorporated cache is freely rewritten when an externalmemory is accessed. This leads to the necessity of an exclusive RAMwhich prevents automatic rewriting of the contents of the cache.

[0023] Another solution is to store a program (commands) or data in anon-cache area so that the program (commands) or data will not becached. But, this scheme prevents the internal RAM from functioning as acache in normal operation mode, the system's processing speed in normaloperation mode is slowed.

[0024] The third problem is that the CPU to be used itself becomesexpensive because the CPU should be a special chip, not ageneral-purpose one, in order to avoid the first and second problems.

[0025] The second prior art suffers the following problems.

[0026] First, the performance gets lower as the reception speed becomeslower. That is, the second prior art is directed to a reception-onlyterminal and the operation clock is always reduced when the terminal isconnected to a communication circuit to receive radio data. Morespecifically, if this prior art is adapted to a terminal having bothtransmission and reception capabilities, the operation clock isdecreased both in transmission mode and reception mode, the performanceis significantly lowered.

[0027] Secondly, operation clocks are needed for two systems for thefollowing reason. Most of general-purpose CPUs do not have two clockinputs, and the clocks of general-purpose CPUs which have two clockinputs are a normal operation clock and a clock for measuring the time.The frequency of the time measuring clock is about 32 KHz, which is veryslow as the reference clock for radio reception. The use of this clockleads to a considerable reduction in reception speed and is nottherefore practical. In this case, an exclusive CPU equipped withanother clock input becomes necessary.

[0028] Thirdly, when the frequency of the reference clock is reduced orthe reference clock is disabled at the time of radio reception, it takestime to return to the normal processing, resulting in a significantreduction in performance. Further, reducing the frequency of thereference clock requires that the OS (Operation System) should handlecontrol of the operation of the radio unit.

[0029] Furthermore, this terminal may fail to properly receive receptiondata for the following reason. It takes time to adjust the timer orclock or time to stabilize the PLL (Phase Locked Loop) or crystaloscillator after the reduction of the clock frequency or the disablingof the reference clock, so that the reception operation cannot beinitiated during such a time. This leads to a significant reduction inperformance. If the timer or the like in the OS gets wrong, the radiounit does not operate properly and some adjustment should be performedto set the radio unit in the proper operation. Such processing needs aconsiderable time to restore the normal reception operation, so thatprocessing of received data may not be completed in time to catch thenext data.

[0030] The third prior art have the following problems.

[0031] First, this prior art copes only with the noise that is generatedby the reference clock used in a radio section. That is, whilegeneration of noise by the CPU's access to the external bus is dominantin an actual radio portable terminal, the third prior art is directed toa measure against noise generated in the radio section and this methodcannot cope with a radio portable terminal which has the radio sectionintegrated with the CPU that performs transmission and reception ofinformation.

[0032] Secondly, the noise that is generated by the CPU's access to theexternal bus has a wide frequency band. The frequency band of the noisegenerated by the CPU's access to the external bus has a width of severalMHz, so that alight alteration of the reference clock cannot eliminatethe influence of noise on the frequency band used in radiocommunication.

[0033] Thirdly, some radio portable terminals do not make accesssynchronous with the reference clock. The timing for memory access isdetermined by the time, not based on the reference clock. When theoperation reference clock is changed, therefore, the timing for memoryaccess is changed and the proper memory access may not be carried out.It is not therefore possible to significantly alter the operation clockof the system.

SUMMARY OF THE INVENTION

[0034] Accordingly, it is a primary object of the present invention toprovide a noise reducing method for a radio portable terminal, whichstores an internal operation program that does not access an externalmemory in a cache incorporated in a CPU in synchronism with datareceived by radio, and allows the radio portable terminal to be operatedonly with access to the internal cache at the time of radio reception,thereby reducing access to the external memory, so that noise toreceived data can be reduced.

[0035] It is another object of this invention to provide a noisereducing method for a radio portable terminal, which can reduce noise bymasking interruption to a CPU before a predetermined program is storedin an internal cache in the CPU, thereby suppressing rewriting of aprogram stored in the cache and preventing access to an external memoryof the CPU.

[0036] To achieve the above objects, this invention employs thefollowing technical structures.

[0037] According to one aspect of this invention, there is provided anoise reducing method for a radio portable terminal having a radiosection for transmitting and receiving radio data, a CPU (CentralProcessing Unit), connected to the radio section and incorporating acache, for performing predetermined data processing, and an externalmemory connected to the CPU, which method comprises the steps of readingan internal operation program runnable only in the CPU from the externalmemory and storing the internal operation program in the cache prior toreception of the radio data; and then executing only the internaloperation program and suppressing access to the external memory duringreception of the radio data, thereby reducing noise.

[0038] According to another aspect of this invention, there is provideda noise reducing method for a radio portable terminal having a radiosection for transmitting and receiving radio data, a CPU, connected tothe radio section, for performing data processing, and an externalmemory connected to the CPU, which method comprises the steps of givinga priority order to individual processes to be executed by the radioportable terminal; and masking an interruption process of low priorityso as not to execute the masked interruption process at a time ofreceiving the radio data, thereby reducing noise at a time of receivingthe radio data.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a diagram showing the structure of a radio portableterminal according to one embodiment of this invention;

[0040]FIG. 2 is a time chart illustrating the transmission and receptiontimings of a radio section in the radio portable terminal shown in FIG.1;

[0041]FIG. 3 is a flowchart illustrating a sequence of processes of theradio portable terminal shown in FIG. 1 from the generation of a requestfor reception of radio data to the end of data reception;

[0042]FIG. 4 is a diagram showing the structure of a radio portableterminal according to another embodiment of this invention;

[0043]FIG. 5 is a flowchart illustrating a sequence of processes of theradio portable terminal embodying this invention in a case wheretransmission and reception are alternately performed; and

[0044]FIG. 6 is a flowchart illustrating a sequence of processes of theradio portable terminal embodying this invention in a case of a radiosystem which has a sufficiently long interval for switching transmissionand reception from one to the other.

[0045]FIG. 7 is a block diagram showing the structure of theconventional radio portable terminal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Preferred embodiments of the present invention will now bedescribed with reference to the accompanying drawings.

[0047]FIG. 1 shows the system structure of a radio portable terminalaccording to one embodiment of this invention. This radio portableterminal comprises a CPU 10, an oscillator 20, a radio section 30 and anexternal memory 40. The CPU 10 operates with an input clock ICLK fromthe oscillator 20 as a reference clock. The radio section 30 sends areception sync signal SYN synchronous with reception of radio data tothe CPU 10, and is connected to the CPU 10 via a data signal line DLN.The external memory 40 performs its data input/output operation underthe control of the CPU 10 via a memory bus MBS.

[0048] The structure of the CPU 10 will now be described in detail. TheCPU 10 comprises a main processing section 11 which performs dataprocessing and analyzes and executes commands, a sub-processing section12 which performs memory management and exception handling, a commandcache 13 as a memory to store commands or a program, a data cache 14 asa memory to store data, a bus interface 15 which controls access to anexternal unit like a memory, a clock controller 16 which sends anoperation reference clock OCLK to the individual blocks, and aninterrupt controller 17 which controls an interruption from outside theCPU 10. The sub-processing section 12 includes an address conversionbuffer (TLB) 121.

[0049] The main processing section 11, sub-processing section 12,command cache 13, data cache 14 and bus interface 15 are mutuallyconnected by an internal bus IBS and implement a data input/outputoperation. The interrupt controller 17 masks interruptions from outsidethe CPU 10 according to preset conditions and gives only the necessaryinterruption to the sub-processing section 12.

[0050]FIG. 2 is a time chart illustrating the transmission and receptiontimings of the radio section in FIG. 1. The time chart in FIG. 2exemplifies the typical transmission and reception timings in athree-channel-multiplexed TDMA (Time Division Multiple Access) system.FIG. 2 shows the transmission and reception timings of the radioportable terminal (mobile station side). The reception operation isperformed first, followed by the transmission operation; reception andtransmission are each executed once in every 20 ms and for 20/3 ms. FIG.2 shows a case where transmission and reception are carried out in slot#O, transmission and reception of data (1) executed first andtransmission and reception of data (2) executed next. The reception syncsignal SYN is generated every 20 ms in synchronism with the receptiontiming.

[0051] The operation of the radio portable terminal in FIG. 1 will beexplained below with reference to an operational flowchart in FIG. 3.FIG. 3 illustrates a sequence of processes from the generation of arequest for reception of radio data to the end of data reception.

[0052] Suppose that a request for reception of radio data has been madewhile the radio portable terminal is performing some process (step S1).First, the main processing section 11 checks the contents of the currenttask (step S2). Then, the main processing section 11 checks if receptionof radio data has priority over the contents of the current task (stepS3). To accomplish this check, a priority order should previously be setto the individual processes.

[0053] When the current task has priority over reception of radio data(N in step S3), the main processing section 11 resumes the current taskand does not perform reception of radio data. When the process that haspriority over reception of radio data is completed (Y in step S3), themain processing section 11 instructs the interrupt controller 17 to maskan interruption having a lower priority than reception of radio data(step S4). This prevents exception handling from occurring by aninterruption having a lower priority than reception of radio data, whichwould otherwise rewrite the program stored in the command cache 13.

[0054] Next, the sub-processing section 12 of the CPU 10 accesses theexternal memory 40 via the bus interface 15, and stores an internaloperation program (module) which does not access the external memory inthe command cache 13 (step S5). After storage of the internal operationprogram, the main processing section 11 of the CPU 10 carries out aprocess of receiving radio data (step S6). The CPU 10 has nothing to dowith the actual reception of the radio data itself which is executed bythe radio section 30, but performs data processing after data reception.When reception of the radio data is completed (Y in step S7), the mainprocessing section 11 unmasks the interruption that has a lower prioritythan reception of radio data (step S8) and returns to the normaloperation after which the CPU 10 processes the received data.

[0055] At the time of data reception, the CPU 10 operates according onlyto an internal operation program stored in the internal command cache 13and does not access the external memory. The CPU 10 can thereforeexecute another process within the capability of a program which isstorable in size in the internal command cache 13.

[0056] Since the CPU 10 used in the radio portable terminal generallygives a higher priority to conditions, such as lower power consumption,lower noise and lower price, over the performance, its internal cachemerely has a small size of about several kilobytes. Therefore, theaforementioned internal operation program that does not access theexternal memory should have a size storable in the small-capacity cache.Therefore, a program to be stored in the command cache 13 as an internaloperation program which does not access the external memory can be madesmall if it is designed to keep a loop in a no operation (hereinafterreferred to as “NOP”) state and leave the loop upon interruption.

[0057] The following will discuss another example of the operation ofthe radio portable terminal.

[0058] As mentioned above, in general, the command cache 13 of the CPU10 used in the radio portable terminal only has a small size of aboutseveral kilobytes. This requires that an internal operation programwhich does not access the external memory should have a size storable inthe small-capacity internal cache. The above operational example ispremised on a case of an internal operation program with a minimum size,and if the size of the internal command cache 13 is large, it ispossible to run a program which executes other processes within itscapability that is limited by the size of the command cache 13. In thiscase, other processes can be executed at the time radio data isreceived, so that the system performance is enhanced significantly.

[0059] A radio portable terminal according to another embodiment of thisinvention will now be described specifically by referring to FIG. 4. Theradio portable terminal shown in FIG. 4 has a structure such that thecommand cache 13 and the data cache 14 of the radio portable terminalshown in FIG. 1 are shared with each other. That is, the command cache13 and the data cache 14 are designed as a single shared cache 18, whichis equipped in a CPU 10A. In this case, it is effective to provide acache lock mechanism which uses, in a fixed manner, an area in the cachewhere a program is stored in order to prevent an internal operationprogram previously stored in the cache from being replaced with anotherprogram. The cache lock mechanism will be discussed below.

[0060]FIG. 5 presents a flowchart of a sequence of processes in a casewhere transmission and reception are alternately performed. The systemstructure is the same as those of FIGS. 1 and 4. The following willdiscuss an example where the system structure shown in FIG. 1 isemployed.

[0061] The flowchart of an operation of receiving radio data is nearlythe same as the one shown in FIG. 3, and radio data is transmittedwithout unmasking an interruption. That is, steps S1 to S7 in FIG. 5 arealmost the same as those in FIG. 3, and step S8 in FIG. 3 is skipped toenter a process of transmitting radio data which will be discussedbelow.

[0062] When a transmission request for radio data is input (step S9), atransmission-mode operation program which is used at the time oftransmitting radio data is loaded (step S11). At this time, a process ofpreventing rewriting of the internal operation program at the time ofreceiving radio data, which has previously been stored in the cache, isexecuted in step S10 between step S9 and step S11. There are two ways(means) to accomplish the prevention.

[0063] The first means uses the cache lock mechanism which fixes an areawhere an internal operation program (module) which runs at the time ofreceiving radio data is stored to thereby prevent rewriting of thatprogram. In this case, what is in other areas in the cache can berewritten freely. The second means stores a transmission-mode operationprogram, which is used at the time of receiving radio data, in anon-cache area. As a transmission-mode operation program, which is usedat the time of receiving radio data, is stored in the non-cache area inthe external memory 40, this program will not be cached so that theinternal operation program at the time of receiving radio data will notbe rewritten with the loaded data. By preventing rewriting of aninternal operation program at the time of receiving radio data which hasbeen stored in advance in the above manner, the receivable state canalways be maintained even in a radio system which implementstransmission and reception of radio data in a short period of time.

[0064] Then, data transmission is carried out (step S12). Astransmission data is not affected much by noise generated from the CPUor other noise at the time of transmitting radio data, the operations ofthe other blocks need not be stopped. To prevent exception handling fromrewriting an internal operation program at the time of receiving radiodata which has been stored in the cache, however, an interruption shouldbe used as masked. In this case, simultaneous execution of anotherprocess requires such restriction that the program should run only atthe time of transmitting radio data. When transmission of radio data iscompleted (Y in step S13), the main processing section 11 unmasks theinterruption (step S14) and returns to step S6.

[0065] Through the above processes, transmission and reception of radiodata are executed alternately.

[0066] Referring to FIG. 6, a description will now be given of asequence of processes in a case where transmission and reception ofradio data are executed alternately by a radio system which has asufficiently long interval for switching between transmission andreception. The system structure is the same as those of FIGS. 1 and 4.The flowchart for reception of radio data is almost identical to the oneshown in FIG. 5, except that radio data is transmitted after unmaskingan interruption (step S8). That is, steps S10 and S14 in FIG. 5 areomitted and step S8 is added between step S7 and step S9.

[0067] As transmission data is not affected much by noise at the timeradio data is transmitted, the normal operation shall take place. Sincethe interval switching between transmission and reception issufficiently long, even if an internal operation program at the time ofreceiving radio data which has been stored in the cache in advance isrewritten, it is still possible to store an internal operation programin the cache again at the time of data reception. It is to be notedhowever that, as mentioned above, simultaneous execution of anotherprocess at the time of data transmission requires such restriction thatthe program should run only at the time of transmitting radio data.Through the above processes, transmission and reception of radio dataare executed alternately.

[0068] As apparent from the above, the summary of this invention will begiven below with reference to FIG. 1.

[0069] When the reception sync signal SYN is input to the CPU 10 fromthe radio section 30, the sub-processing section 12 loads an internaloperation program which access no external memory from the externalmemory 40 into the command cache 13. At this time, the interruptcontroller 17 is instructed to mask an interruption of a low priority inorder to prevent data stored in the command cache 13 from beingrewritten by exception handling which is originated from anotherinterruption. This eliminates the need to acquire a command and data forexecuting the internal operation program from the external memory 40during radio reception. This decreases the number of accesses to theexternal memory 40 by the CPU 10, thereby ensuring reduction in noisewhich affects the radio section 30 can be decreased. It is also possibleto execute a process other than reception inside the CPU 10 during radioreception.

[0070] It should of course be apparent to those skilled in the art thatthe present invention is not limited to the above-described embodimentsbut may be modified in various other forms without departing from thespirit or scope of the invention.

[0071] As described above, this invention has the following advantages.

[0072] The first advantage is that noise which affects the radio sectioncan be reduced without considerably lowering the system performance.This is because an internal operation program which does not access theexternal memory only in reception mode is executed just in the CPU insynchronism with the radio-received signal. As the program runs in theCPU at the time of reception, therefore, noise can be reduced and thenormal operation takes place in transmission mode so that theperformance is not reduced much.

[0073] The second advantage is that reduction in radio receptionsensitivity is prevented by storing an internal operation program in thecommand cache at the time of radio reception. This is because storing aninternal operation program in the command cache at the time of radioreception reduces the number of accesses to the external memory by theCPU, which can reduce noise generated by access to the external memory.

[0074] The third advantage is that reduction in radio receptionsensitivity is prevented by masking an interruption of a low priorityfor the following reason. The masking process can prevent exceptionhandling from being executed by generation of an interruption, whichwould otherwise rewrite the program previously stored in the commandcache. If exception handing occurs, the above process switches thecommand cache so that at the time of performing a process of receivingradio data again, a program should be read by re-accessing to theexternal memory. As reception of radio data is carried out withpriority, the other blocks will not function, thus reducing noise.

[0075] The fourth advantage is a capability of preventing insufficiencyof the performance or significant reduction of the system performanceafter reception of radio data for the following reason. As the receptionsensitivity is enhanced by reducing noise without disabling theoperation reference clock of the CPU at the time of receiving radiodata, it is possible to move to a post-reception process right away.Generally speaking, when the operation reference clock is disabled, itneeds time to adjust the timer or clock or time to stabilize the PLL orcrystal oscillator to become stable after the reduction of the clockfrequency or the disabling of the reference clock, so that the CPUcannot stably perform processing immediately after the operationreference clock is disabled.

[0076] The fifth advantage is that the radio portable terminal can beconstructed using a general-purpose CPU because the system is operablewith a general-purpose CPU with an internal cache and requires noexclusive CPU having a ROM or RAM incorporated therein. Further, thesystem can be constructed in accordance with an arbitrary cache size byallowing a program whose size matches with the capacity of the internalcache at the time of receiving radio data. Because there is no built-inexclusive ROM, it is possible to easily correct or change a program.

[0077] The sixth advantage is that even a small portable terminal can bepermitted to receive radio data for the following reason. Because noiseat the time of reception is reduced, even a small portable terminalhaving its radio section arranged close to the CPU can receive radiodata without reducing the reception sensitivity of the radio section.

[0078] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristic thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

[0079] The entire disclosure of Japanese Patent Application No.10-305837 (Filed on Oct. 27^(th), 1998) including specification, claims,drawings and summary are incorporated herein by reference in itsentirety.

What is claimed is:
 1. A noise reducing method for a radio portableterminal having a radio section for transmitting and receiving radiodata, a CPU, connected to said radio section, for performing dataprocessing, and an external memory connected to said CPU, said methodcomprising the steps of: giving a priority order to individual processesto be executed by said radio portable terminal; and masking aninterruption process of low priority so as not to execute said maskedinterruption process at a time of receiving said radio data, therebyreducing noise at a time of receiving said radio data.
 2. The noisereducing method according to claim 1, wherein said CPU distinguishes areception period for said radio data and other periods based on a syncsignal associated with reception data sent from said radio section. 3.The noise reducing method according to claim 1, wherein whentransmission/reception of said radio data is repeatedly carried out, atransmission-mode operation program runnable at a time of transmittingsaid radio data is stored in said external memory; and a cache in saidCPU is locked at a time said transmission-mode operation program isexecuted.
 4. The noise reducing method according to claim 1, whereinwhen transmission/reception of said radio data is repeatedly carriedout, a transmission-mode operation program runnable at a time oftransmitting said radio data is stored in a predetermined non-cache areaprovided in said external memory.
 5. The noise reducing method accordingto claim 2, wherein at a time of transmitting said radio data, saidinterruption process is unmasked to thereby provide a normal operation.